Method and apparatus for peening the inside of tubes and other hollow bodies



Feb. 1, 1949. T. ROBINSON 2,460,657

METHOD AND APPARATUS FOR PEENING THE INSIDE' OF TUBES AND OTHER HOLLOW BODIES 2 Sheets-Sheet 1 Filed Dec. 22, 1944 X Z V m w 5 r A A M w M WM W\ k)? Y T- ROBINSON METHOD AND APPARATUS FOR PEENING THE INSIDE OF TUBES AND OTHER HOLLOW BODIES 2 Sheets-Sheet 2 Feb. 1, 1949. 2,460,657

Filed Dec. 22', 1944 INVENTOR. 77/0/1145 Foam/6a MAX/$4M ATZUENE'Y I Patented Feb. 1, 1949 METHOD AND APPARATUS FOR. PEENING THE INSIDE OF TUBES AND OTHER HOL- LOW BODIES Thomas Robinson, New York, N. Y., assignor to Lancaster Processes, Inc., New York, N. Y., a corporation of New York Application December 22, 1944, Serial No. 569,382

24 Claims.

The present invention relates to method and apparatus for peening metal surfaces, and particularly for peening the inner surfaces of hollow members.

The beneficial results obtained by peening metal surfaces have been known since the early days of metal working. The ancient sword makers and village blacksmiths long ago recognized that greater strength could be obtained by cold hammering or peening the surfaces of parts subject to heavy stress. More recently it has been discovered, or rediscovered, that peening greatly increases the resistance to fatigue and resistance to destructive corrosion.

The peening of external surfaces has been widely practiced and presents no particular difflculties. However, the peening of inside surfaces of hollow bodies, as for example, the inside of a tubular member, has always presented a difiicult' problem as the inaccessibility of such surfaces prevents the use of available peening methods. In many instances it is even more desirable to peen the inside surface of an article than the outside surface; For example, by peening the inner surface of a pip, its resistance to scaling and corrosion, as well as its resistance to erosion, can be greatly increased. However, no means has heretofore been available for satisfactorily peening the inner surfaces of pipes or other hollow articles.

It is an object of the present invention to provide a novel method of peening metal surfaces. A further object of my invention is to provide a novel method of peening the inside surfaces of tubes and other hollow articles. The term tube is used generically in the present specification and claims to include pipes, casings, piling, and other tubular members.

Another object of my invention is to provide a method and apparatus for peening the inside surfaces of tubular and other hollow members efficiently, rapidly and economically on a commercial scale. A further feature of the invention is that the intensity and distribution of the peening action is subject to control, so that the entire inner surface can be peened uniformly to any desired degree. Alternativey, the peenin action can be confined to selected areas or can be of greater intensity or duration in certain areas than in others.

Fig. 2 is a cross section taken approximately 2 on the line 2-2 in Fig. 1, and showing one of the supporting and vibrating units of the apparatus in end elevation. I

Fig. 3 is a side elevation of one of the supporting and vibrating units.

Fig. 4 is an enlarged cross section through a tube being peened, and showing one form of peening means inside the tube.

Fig. 5 is a fragmentary longitudinal section through one end of the tube and showing another form of peening means. Fig. 6 isa cross sectiontaken approximately on the lines G6 in Fig. 5.

In accordance with my invention the inside surface of a hollow member is peened by introducing peening elements into the interior of the hollow member, and vibrating the member to produce repeated impact between the peening elements and the inner surface of the hollow member. The peening elements are of such nature as to produce a true peening-action such as that produced by a peening hammer, as distinguished from grinding, scouring or abrading. The impact surfaces of the peening elements should hence be smooth and should preferably be surfaces or double curvature. The peening elements may be separate members, for'example hard steel balls similar to those used in ballbearings, or may be connected or integralv with one another, as for example the convolutions of a helical spring. In accordance with my preferred method, the peening elements are loosely confined in the hollow body to be treated, so that in a static condition they rest on the inner surface of said body. Upon the application of vibrational energy to the hollow body, preferably of a frequency in the sonic range, 1. e. in the range of audible sound, the peening elements and the wall of the hollow body are activated to produce 4 rapidly recurring impacts of the peening elements with the inner surface of the member being treated. The nature of the vibration should be such as to cause relative reciprocating movement of the peening elements, which is predominately at substantially right angles to the inner surface of the hollow member ratherthan sliding or tangential motion. The rapidly recurring impacts of the peening elements quickly and effectively peen the inner surface of the hollow member. By effecting relative movement of the member being treated and the peening elements to cause the elements to strike in different places on successive impacts, the entire area to be treated can be peened either uniformly or differentially, as desired. For example, the member can be turned while being vibrated so that different areas are successively presented to the action of. the peening elements and the indi-- vidual elements are caused to strike the surface at different points. The intensity of the peen- 3 ing action may be controlled by the frequency and amplitude of vibration and by the nature of the peening elements and the duration of treatment. The peening of the inner surface of the member is thus subject to full and effective control. 1

In the accompanying drawings there is shown 7 by way of example, apparatus for peening the inside surface of a pipe or tube Ill. The apparatus shown in Figs. 1 to 3 comprises peening elements disposed inside the tube, and means for supporting the tube for reciprocatory vibration, and for applying vibrational energy to the tube while thus supported. Means is also provided for rotatin the tube while being vibrated, so that the inside of the tube is peened throughout its peripheral extent. While the functions of supporting, vibrating and rotating the tube may, if desired, be performed by individual means, the embodiment of the apparatus illustrated in the drawings provides unitary means for concurrently performing all three functions.

By reference to Fig. 1, it will be seen that the tube is supported by a plurality of units, indicated generically by the reference numeral ll. These units are preferably identical with one another and are set at spaced points to support the tube throughout its length. Each of the units comprises means for resiliently supporting the tube, and means for supplying periodic impulses to set the resiliently supported tube in vibration. The resilient support is provided by one or more elongated resilient members l2, shown in the form of a stack of bars of rectangular cross sec.-

tion. The bars I! are held firmly at their ends by a suitable frame or housing iii. The central portion of the bars is free to vibrate and carries a clamp or yoke M provided with a bearing l5 for holding the tube being treated. The yoke l4 also carries the armature i6 of an electro-magnetic motor, the stator I! of which is mounted on the frame or housing l3, for example, by means of downwardly extending brackets l8. Vertical adjustment of the stator l! to vary the gaps between the stator and the armature is provided by adjusting screws l9.

Provision is made for supplying alternating or pulsating electric current of the desired frequency to the electromagnetic motor, to apply periodic impulses to the armature l6 and thereby produce vibratory movement of the resiliently supported tube ID. The frequency of the current is correlated to the natural frequency of vibration of the vibratory system, comprising the resilient members l2, the yoke l4 and tube Hi, to produce vibratory movement of the desired amplitude. Preferably the electric current is supplied by a source of variable frequency so that the frequency can be adjusted to the natural frequency ofthe resiliently supported tube or other member being treated. The amplitude and frequency of vibration of the tube should be sufilciently high that the acceleration of the tube is greater than gravity. The vibratory motion of. the tube produced by the apparatus shown in the drawings is reciprocating motion in a direction crosswise of the tube.

The transverse vibration of the tube activates the peening elements disposed inside the tube, and produces rapidly recurring impact of said elements with the inner surface of the tube. In the embodiment illustrated in Figs. 1 to 3 of the drawings, the peening elements comprise the convolutions of a spiral spring 20, which extends throughout the length of the tube. The GQ WO- lutions of the helical spring 20 provide peening surfaces of double curvature similar to the surface of a peening hammer. The flexibility of the spiral spring core assures contact of the convolutions of the spring with theinner surface oi the pipe throughout its length, despite any slight irregularity in the surface. At the same time, the action of the spring tends to smooth out any irregularities, to produce a more even surface. The helical spring 20 is of a lesser diameter than the inner diameter of the tube and is confined loosely in the tube, so that it rests freely on the lower inside surface of the tube in static condition. Vibration of the tube by means of the units described above, transmits vibrational energy to the helical spring, so that the spring is also caused to vibrate. The reciprocatory vibration of the tube in a direction transverse to its axis, causes the peening elements to strike the tube at approximately right angles to its surface. A true peening action is thereby produced without excessive scouring or abrasion. As the peening elements are distributed throughout the length of the tube, and as the tube is vibrated throughout its length by the units H, the inner surface of the tube is peened simultaneously from one end to the other. By rotating the tube about its longitudinal axis, all portions of the inner surface of the tube can be quickly and effectively peened.

In the preferred embodiment of my invention, the tube is automatically rotated while being vibrated. As shown in Figs. 1 to 3, rotation of the tube is produced by extremely simple mechanism comprising a flexible strap 2| extending up over the tube held in the bearings l5, and having one end 22 of the strap anchored to the frame of the unit A yielding downward pull is exerted on the other end of the strap 2| by a spring 23. The strap 2|, while sufliciently flexible to conform to the tube, is preferably substantially non-extensible, and is either provided with a friction lining or is made of material providing suitable frictional engagement with the surface of the tube. By reason of this frictional engagement and the manner in which the strap is anchored solidly at one end and resiliently at the other, vibration of the tube by the units results in concurrent rotation of the tube about its longitudinal axis.

While the bearings l5 may, if desired, completely surround the tube, they are shown as half bearings, since the strap 2| serves as the upper half of the bearings as well as the means for rotating the pipe. The spring 23 should be sufficiently strong to hold the tube firmly seated on the bearings I5. The strap 2| is preferably provided with a quick acting fastening device at one end or the other, for example, at the end held by the spring 23, so that the straps can be released to permit removal of a tube after treatment and the insertion of a new tube. The combination of the half bearings 5 and the straps 2|, thus provides for rapid loading and unloading of the apparatus.-

The rotation of the tube l0 concurrently with its vibration results in peening the inner surface throughout the length of the tube and throughout its peripheral extent. The entire inner sur-- face of the tube is thus uniformly peened. However, it will be understood that by controlling the rotation of the tube and the position of the peening elements, the peening action may be confined to selected areas, or certain portions of the surface may be peened more than others.

' rotated by its engagement with the tube.

' ano es? Y the tube on successive revolutions. This relative movement of the tube and the. spring is equivalent to relative movement in a longitudinal direction, so that the points of contact are continually shifted and the formation'of distinct rings or depressions in the inner surface of the tube is avoided. Preferably the inner diameter of the tube should be other than an integral multiple of the outer diameter of the helical spring 20. If desired, the peening elements can be moved ments may also be greater than the amplitude of vibration of the tube, since the peening elements may have greater freedom of movement than the tube. The increased amplitude of the peening elements results in greater force of impact of the elements with the tube,.and hence in still greater effectiveness of the treatment.

While the drawing illustrates the peening of a straight tubular member, it will be understood that the method and apparatus in accordance with my invention are equally applicable to the peening of other hollow members including those of irregular shape. It will also. be understood that the invention is in'noway limited to the particudrawings, but may be varied as desired within the scope of the appended claims.

axially of the tube. during vibration, for example, by inclining the. direction of vibration of the tube to its longitudinal axis, so that the peening elements are moved axially of the tube by its vibration.

Byusi g the requirednumber of supporting and vibrating units ii, a tube of any desired length may be peened by the apparatus in ac cordance with the present invention. Preferably the units are supported in such manner that they can be moved to vary the spacing between. them. For example, in treating a heavier tube,

it maybe desired to have the units closer together. The units are preferably mounted on vibration insulating supports, for example, shear 2o 1. A method of peening the inner surfaceof a '25 face of said member.

type insulators, as illustrated at 24, to reduce the transmission of vibration to thefoundatlom The nature of the peening element's'in the tube may be varied as desired. In Fig. 4, there is shown an embodiment of my invention in which the peening means comprises a helical spring which is weightedor loaded-by an inner core 25, to increase its effectiveness. The inner core 25, may for example, be in the form of a rod, a hollow tube, or another spring. I

In Figs. 5 and 6, there is shown a further form of my invention in which the peening means comprises a multiplicity of spherical balls 26. The balls 26 are preferably formed of hard, elas tic material, such as steel, and may for example be similar to the balls used in ball bearings. The tube is partially filled with the balls, leaving room for vibratory movement of the balls inside the tube. A suitable cap\ 2| secured in place by set screws or other fastening means 28 is provided I on each end of the tube to retain the balls in the By reason of'the resilient nature of the peening means inside the tube, whether in the form of individual balls, a helical spring, or other of step and continually collide with one another. By suitably selecting the proportions and material of the peening elements, their natural frequency of vibration, may be made higher than that of the tube, so that a still greater number' of impacts is obtained. The amplitude of vibration of the peening ele- What I claim and desire to secure 'by Letters Patent is:

hollow member, which, comprises introducing peening elements in said hollow member and vibrating said member to produce repeated impact ,,between said peening elements and the inner surlii lar apparatus shown by way of example in the '2. A method of peening the inner surface of a hollow member, which comprises introducing peening elements in said hollow member, vibrating said 'member'to'produce repeated impact be- 30 tween said peening elements and the inner surface of said member and turning said. member during treatment to subject different portions of said surface ments' x t 3. A method of peening the inner surface .of a hollow" member, which comprises introduci peening elements in said hollow member, vibrating said member to produce repeated impact between said peening elements and the inner surace of said member, and producing relativer'noVe;

to the. peening action of said 'element between said member and elements to cause said peening elements successively to strike dif- 5. A method of peening the inside of a tube,

which' comprise's introducing peening elements in said tube, vibrating said tube to produce repeated impact between said peening elements and the inner surface of the tube, and concurrently rotating said tube.

'which comprises introducing peening elements in said tube and imparting reciprocatory vibratory motion to said elementsto produce repeated imface of the tube.

'7. A method of peening the inside of a hollow member, which comprises placing inside said -member a plurality of. peening elements having impact surfaces of double curvature and vibrating said-member to produce repeated impact between said peening elements and the inner surface of said member. 8.'A method of peening the inside of a hollow member, which comprises introducing peening elements inside said member and vibrating said -member at a frequency in the sonic range, to

produce repeated impact between said peening elements and the inner surface of said member.

9. A method of peening the inside of a tube, which comprises introducing peening elements 6. A method of peening the inside'of a tube,-

pact between said elements and the inner surinside said tube, said peening elements being distributed throughout the length of the tube, and vibrating the tube throughout its lensth to produce repeated impact between said peening elements and the inner surfaceof the tube.

10. A method of peening the inside of a tube,

which comprises placing in said tube a flexible core having a plurality of peening surfaces, and vibrating said tube to produce relative reciprocatory movement between said tube and core, and repeated impact of said peening surfaces with the inner surface of said tube.

11. A method of peening the inside of a tube. which comprises placing in said tube a helical spring of lesser diameter than the inside diameter of said tube, and vibrating said tube to produce repeated impact between the convolutions of said helical spring and the inner surface'of said tube.

12. A method of peening the inside of a tube, which comprises rotatabl'y supporting said tube,

introducing peening elements in said tube, and

vibrating said tube to produce repeated impact between said peening elements and the inner surface of the tube, and concurrently produce rotation of said'tube.

' 13. A method of peening the inside of a tube, which comprises placing in said tube a helical spring of lesser diameter than the inside diameter of said tube, vibrating said tube to produce repeated impact between the convolutions of said helical spring and the inner surface of said tube, and rotating said spring and tubes at difierent rates to vary the points of impact.

14. A method of peening the inside of a hollow member, which comprises introducing peening means into the interior of said member, applying vibrational energy to said member and to said peening meansto produce Ieciproca-tory vibration of, and impact between, said means and said members, the natural frequency of vibration of said peening means being different from the frequency of vibration of said hollow member.

15. A method of peening the inside of a hollow member, which comprises introducing peening' means into the interior of said member, vibrating said member and thereby producing reciprocatory vibration of said peening means and impact of said peening means with the inner surface of said member, the amplitude of vibration of said means being greater than the amplitude of vibration of said member.

16. A method of peening the inside of a hollow member, which comprises loosely confining a multiplicity of spherical balls in said member and vibrating said member to produce impact between said balls and the inner surface of said hollow member.

17. Apparatus for peening the inside of a tube, which comprises peening elements adapted to be inserted in said tube and a plurality of units cooperating to vibrate said tube throughout its length to produce repeated impact between said peening elements in. the tube and the inner sur-' face of said tube.

18. Apparatus for peening the inside of a hollow member, which comprises peening elements adapted to be inserted in said tube, means for vibrating said member to produce repeated impact between said peening elements in the tube and the inner surface of said member, and means for rotating the member being treated.

19. In apparatus for peening the inside of a tube, the combination of peening elements 8 adapted to be inserted in said tube, a bearing for supporting the tube, means for vibrating said bearing to apply vibrational energy to said tube and produce impact between said peening elements and the inner surface of. said tube, and means for rotating said tube during vibration, comprising a. flexible member anchored at one end and extending around said tube, and resilient means acting on the other end of said flexible member to urge said member into frictional contact with said tube.

20. Apparatus for peening the inside of a hollow member, which comprises peening elements having smooth impact surfaces and adapted to be inserted in said hollow member, and means for vibrating said hollow member to produce repeated impact between said peening elements and the inner surface of said member, a

21. In apparatus for peening the inside of a tube, the combination of peening elements adapted to be inserted in said tube, a half bearing for supporting the tube, means for vibrating said bearing to apply vibrational energy to said tube and produce impact between said peening elements and the inner surface of the tube, and a, flexible member extending over said tube to hold said tube in said half bearing and to rotate said tube while being vibrated.

22. In apparatus for peening the inside of a tube, the combination of peening elements adapted to be inserted in said tube, means for vibrating said tube to produce repeated impact between said peening elements and the inner surface of the tube and actuated by said vibratory motion of the tube to rotate thetube about its 24. In apparatus for peening the inside of a tube, the combination of a spiral spring adapted to be inserted lengthwise in said tube, a core inside said spiral spring, and means for vibrating said tube to produce impact between the convolutlons of said spring and the inner surface of the tube.

THOMAS ROBINSON.

RarERENcns cr'ran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 141,247 Weldon July 29, 1873 703,415 Hehr July 1, 1902 751,506 Hatfield Feb. 9, 1904 837,309 Kyle Dec. 4, 1906 937,180 Ridd Oct. 19, 1909 1,050,534 Hart et al Jan. 14, 1913 1,481,741 Ray Jan. 22, 1924 1,770,847 Erickson July 15, 1930 1,833,025 Langenberg Nov. 24, 1931 1,851,932 Fabens Mar. 29, 1932 FOREIGN PATENTS Number Country Date 306,936 Great Britain Jan, 25, 1929 

